1. Field of the Invention
The present invention relates to a composite display apparatus achieved by miniaturizing the whole apparatus having an image-pickup optical system for capturing light from image information of the outside to form an image on an image pickup device and a display optical system for observation of image information displayed on a display device such as a liquid crystal display. More particularly, the invention is suitably applicable to apparatus called a head-mounted display (HMD) and a goggle type display.
2. Related Background Art
There have been suggested heretofore apparatus in which a small CCD camera is mounted on the HMD and which is arranged to display image information obtained through the small CCD camera on the HMD as it is, and apparatus for processing the image information obtained through the small CCD camera to convert the information to some image information to display it on the HMD. Further, a variety of suggestions have been made heretofore as to a seethrough type HMD (which is an HMD in the structure capable of directly observing light from the outside at the angular magnification 1) among the HMDs.
The HMD of this type will have a parallax if there is a difference between the eyeball optic axis of the display optical system for observation of image information displayed on the display device of HMD and the optic axis of the CCD camera (the image-pickup optical system) for imaging the image information of the outside on the CCD surface. Devices having both the image-pickup optical system and the display optical system without a parallax are suggested in Japanese Laid-open Patent Applications No. 4-22358 and No. 5-303053.
In the display optical system proposed in Japanese Laid-open Patent Application No. 4-22358, light emitted from a small liquid crystal display travels via a flat half mirror to be guided to the eyeball by an eyepiece. On the other hand, the image-pickup optical system is so arranged that the light from the outside travels via the flat half mirror to be focused on the small camera. Since this flat half mirror was located at 45.degree., the apparatus tended to become large. In addition, because there is the eyepiece in front of the eyeball, the seethrough optical system cannot be established.
Japanese Laid-open Patent Application No. 5-303053 discloses a configuration capable of establishing the seethrough optical system, but there was such a tendency that the optical system was complex and the apparatus became very large.
The parallax will appear if there is a difference between the eyeball optic axis of the display optical system for observation of the image information displayed on the display device of HMD and the image-pickup optic axis of the image-pickup optical system (CCD camera) for focusing the image information of the outside on the CCD surface. When the half mirror is used to align the optic axes of the both image-pickup optical system and display optical system with each other in order to eliminate this parallax, part of the light from the display device passes through the half mirror to be incident onto the CCD surface of the image-pickup optical system in some cases. The light from the display device, if mixed with the image information from the outside formed on the CCD surface, becomes flare (noise), thus becoming a cause of degrading the quality of image information of the outside.
There are the following demands for the composite display apparatus such as the HMD as described above; the whole apparatus is so compact and lightweight as to be mounted on the head part of an observer, the quality of images by the display optical system and the image-pickup optical system is high enough, no parallax occurs, and the seethrough optical system can be established.